Multi-objective Optimization of Injection-Production Parameters Based on Interlayer Interference Evaluation in Shale Low Permeability Interbedded Reservoirs

This study focuses on a reservoir in eastern China with rich hydrocarbon resources, characterized by the vertical superimposition of shale oil and tight interbedded layers. The lower low-permeability sandstone layers have thin pay zones, poor petrophysical properties, and low movable reserves. The upper shale oil layer is heavily fractured, limiting the effectiveness of horizontal well development. Separate development of individual layers yields poor economic performance, leading to the proposal of a development strategy that integrates shale oil and low-permeability sandstone interlayers. Due to the significant heterogeneity of the shale oil and low-permeability sandstone composite reservoir, interlayer interference and low waterflooding efficiency are major challenges. This study investigates the critical threshold values of key control parameters, such as the minimum principal stress difference between layers, permeability contrast, and injection-production ratios, aiming to reduce interlayer interference and enhance recovery. Unconventional hydraulic fracturing techniques are employed to analyze the capillary imbibition efficiency in the shale oil layer and the fracture propagation during water injection-driven displacement in the low-permeability sandstone. The study also utilizes a coupled geomechanics-fluid flow numerical model, introducing an interlayer interference coefficient to quantify the degree of interference under combined development. The NSGA-II algorithm is used to optimize key parameters. Numerical simulations on Block X demonstrate that commingled depletion development results in higher interlayer interference compared to alternating development, which is greater than sequential backflow development. Under varying geological and engineering conditions, cumulative oil production ranges from 15,000 m3 to 43,000 m3, with interlayer interference coefficients fluctuating between 0.46 and 0.93. A Pareto front plot of cumulative oil production versus interlayer interference coefficients is divided into three regions, identifying the maximum cumulative oil production scheme, the optimal scheme, and the scheme with minimal interlayer interference.